Summary of El and JSTL precautions

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EL Use expressions （5 One problem ） JSTL Use a label （5 problem ） What is? EL. It can be used for ？ EL full name Expression Language stay JSP Use page Lattice formula ${ expression } Examples ${requestScope.customer.id} function ： 1. Only four domain objects were taken out to display the attribute data

(pageContext.request.session.application)

2. Take out the request parameter data and display

<% request.setAttribute(“person”,new Person(“xfzhanag”,18)); %> Map<String,Person> map=new HashMap<String,Person>(); map.put(“A”,new Person(“AA”,12)); map.put(“”B”,new Person(“BB”,13)); map.B.age

{requestScope.person.name}; {requestScope.person[‘name’]}; List The second data in it <%

<% List list=new ArrayList(); list.add(“a”); list.add(“b”); list.add(“c”); request.setAttribute(“List”,list);

%>

{requestScope.List[1]}; {requestScope.List[‘name’]};

My age ：<requestScope.person.name><br/> // What's convenient ？ Why is there a bracket ？ /* A situation ？ ${requestScope[‘my person’].name}; map.put(“my person”,new Person(“Xxx”,12));

*/ EL Operations that can be performed ？ Arithmetic operation (+,-, * ,/ ,%) Relationship between operation (>,<,==,!=) Logical operations (&&,||) empty operation ( Infer whether a data is empty ) （null, An empty string , Empty set ）

{empty name}<br>

Three item conditional operation {requestScope.person.age>18 ? ‘ adult ’ : ‘ A minor ’ }

fmt:formDate SQL Tag library sql http://sun.com/jsp/jstl/sql sql:query xml Tag library xml http://sun.com/jsp/jstl/fmt x:forBach Function tag library fn http://sun.com/jsp/jstl/function fn:split Why use JSTL？ stay jsp Use in jsp Script +jsp Expressions can also do circular output , too troublesome EL Can't do traversal work JSTL Be able to do this and work with jsp and html The labels of can be combined very well JSTL High speed entry 1. Import JSTL dependent jar package ： jstl.jar standard.jar

2. stay jsp Import... Into the file JSTL Of c Tag library <%@ taglib uri=”http://java.sun.com/jsp/jstl/core” perfix=”c”

%>

3 <% List<String> list=new ArrayList<String>(); list.add(“A”); list.add(“B”); list.add(“C”); request.setAttribute(“list”,list);

%> <c:forEach items=”

jstl How to do process control ？ c:if( A conditional inference ) c:choose c:when

// demand 1： Suppose I'm younger than 18 Export minors （ In red ） <c:if test=”${person.age<18}”> <font color=”red”> minors </font> </c:if>

demand 2： Suppose you are older than 60, It outputs ’ Old man ‘ Suppose you are younger than 18, It outputs ” Small fart child ” Other . It outputs ” adults ” <br/> <c:choose> <c:when test=”${person.age>60}”> Old man

</c:when> <c:when test=”${person.age<18}”> Small fart child

</c:when> <c:otherwise> adults </c:otherwise> </c:choose> jstl How to traverse ？ <% Map<String,Person> map=new

HashMap<String,Person>(); map.put(“1”,new Person(“AA”,23)); map.put(“2”,new Person(“BB”,23)); map.put(“3”,new Person(“CC”,23)); map.put(“4”,new Person(“DD”,23)); map.put(“5”,new Person(“EE”,23)); map.put(“6”,new Person(“FF”,23)); request.setAttribute(“personMap”,map); %> <h3> Display the data in a table </h3> <table border=”1″ style=”width:300px”> <tr> <td>ID</td> <td> full name </td> <td> Age </td> </tr> <c:forEach items=”{item.key}</td> <td>

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